1. Field of the Invention
The present invention relates to image forming systems capable of printing copies of image data read by a copier using a plurality of copiers on a job-sharing basis, and relates to methods for controlling image forming systems.
2. Description of the Related Art
A function of printing copies of image data read by one copier using a plurality of copiers by sharing the copies among the plurality of copiers is well known. Such a function is referred to as, for example, cascade copying. When cascade copying is used for printing, ten copies of an original, for example, images represented by image data read by a scanner of a copier A can be printed by each of the copier A and a copier B in two groups of five. Thus, printing can be finished in half the time of printing using only one copier.
When an error such as a paper jam, a run out of paper error, and a run out of toner error that prevents continuation of the printing process occurs in one of the copiers during cascade copying, the rest of the copies that were to be printed by the copier having the error can be printed by the other copier instead (substitution copying; see, for example, Japanese Patent Laid-Open No. 2003-198781).
This function will now be described in detail with reference to FIGS. 1A to 1D. For example, a user has an original document of one hundred pages, and wants to make ten copies of the document (FIG. 1A). When the user uses the above-described cascade copying function, image data read by the copier A is sent to the copier B, and each of the copier A and the copier B prints five copies of the document (FIG. 1B). When an error such as a paper jam occurs in the copier B at the moment of finishing printing of the eightieth page of the third copy, substitution copying is performed (FIG. 1C). More specifically, when the copier A receives an error notification from the copier B, the copier A is set to print three extra copies that have not been printed by the copier B in addition to the five copies already allocated to the copier A (FIG. 1C). That is, the copier A prints the copies that have not been printed by the copier B instead of the copier B. In the above-described technology, eight copies of the document are printed by the copier A, and two copies and eighty pages that do not constitute a complete copy are printed by the copier B when the printing is finished. That is, eighty extra pages are unnecessarily printed by the copier B due to substitution copying carried out in response to the occurrence of an error (FIG. 1D) although ten copies of one hundred pages were originally intended to be printed.
As described above, when substitution copying is performed in units of copies upon the occurrence of an error during cascade copying, extra outputs that do not constitute a complete copy can be produced.